So I have a 2003 Nissan Xterra for the last 2 days when I am sitting idle for more than just a few minutes I have noticed my temperature gauge rise. It shows my car running super hot. As soon as I start driving again the temperature drops back to normal in a matter of 10 seconds or less. What could be causing this?

You my friend, have a bad thermostat. It sits in a housing at the front of your motor, you’ll know where because its where one of the big hoses from the radiator connect to the motor. You see what happens is when the motor is idle, the thermostat isn’t letting enough coolant run through the motor, and when you step on the gas the pump pushes harder and opens the thermostat, forcing the coolant through. It is an easy job. Disconnect the hose, and there are two bolts holding the housing to the engine. Remove the housing and the thermostat just sits there, take it off, pop the new one on, bolt the housing back on connect the hose, and your problem should be fixed.

This is not a stuck thermostat problem. If it were, the engine would start to overheat at all operating conditions. But the overheating only occurs when sitting still idling.
This points to a problem with the electric radiator cooling fan.

When moving down the road enough air is forced thru the radiator to prevent the engine from overheating. As soon as the vehicle sits and idles, and if the radiator fan doesn’t come on, the engine starts to overheat.

Thats right. Check for a bad fuse or relay if the fan isn’t working. If that isn’t it then then check if its grounded properly. Also there is a switch that tells the fan when to kick on, but I’m not sure where it would be on that car. Trace the wires. If the switch is bad, thats your problem.

Hmmmmm…thanks everyone. I do have to tell you also that I had my thermostat replaced no more than 3 years ago. I took my truck to the dealership with a similar problem and they told me it was a thermostat stick and charged me an exorbitant amount to fix the problem. I think I am going with an independent shop this time. Not sure it was truly a bad thermostat the first time, but I am thinking that since the thermostat has been fixed once it probably isn’t bad again. I think I am going to check the fan first should be easy to check. Still open to more opinions.